1. Field of the Invention
This invention relates to an apparatus and method for forming an intimate, substantially uniform layer of a coating material on a substrate or wafer. More specifically this invention relates to means for applying a vacuum in the vicinity of a controlled gap formed between a chamber and edge of a rotating substrate which removes excess coating material formed around the edge of a substrate during rotation thereof by a rotating or spinning means.
2. Description of the Prior Art
It is known in the prior art to utilize apparatus for rotating or spinning a substrate and during such rotation or spinning thereof to apply a controlled amount of photoresist coating material onto the spinning substrate to form a thin substantially uniform film of coating material on a selected surface of a substrate. Such apparatus are generally known as photoresist spinners. Typical of such apparatus is a model 101 Photoresist Spinner sold by Headway Research, Inc, Garland, Texas.
Methods are known for insuring that the film formed on the surface of a substrate is free of entrapped pockets of air during rotation. One method for accomplishing the above, which is disclosed in U.S. Pat. No. 3,862,856, is to cause a platform or platen surface, to which a substrate is attached, to oscillate in a shaking motion to produce a shearing force to lift minute pockets of air trapped at the liquid surface. The motor construction provides for mounting the substrate on a vacuum chuck with an output shaft holding the chuck having a liquid slinger to prevent the coating material from draining into the motor.
U.S. Pat. No. 3,974,797 discloses another known method for rotating a plurality of semiconductor slices in a support fixture. Initially, a support fixture containing semiconductor slices is dipped into a quantity of light sensitive or photoresist material or the semiconductor slices are sprayed with the photoresist material. The support fixture having the semiconductor slices containing the deposited photoresist material is rotated about its axis at a predetermined rate for a predetermined time in order to uniformly distribute a predetermined thickness of the light sensitive material over the entire surface area of the semiconductor slices.
Use of spinning apparatus for coating material on surfaces other than substrates or wafers is well known in the art. Typical of such art is U.S. Pat. No. 4,096,295 for coating lens or sheets wherein the items to be coated are placed into a tank containing fluid coating material, removed and spun to remove excess coating material from the sheet or lens surface.
U.S. Pat. No. 3,359,132 discloses a method of coating circuit paths or printed circuit boards with solder by submerging a printed circuit board having a flux applied thereto into a molten solder bath and then withdrawing the same from the bath and rapidly spinning the same to remove excess solder and form a smooth uniform coating having maximum surface adhesion.
U.S. Pat. No. 4,075,974 discloses apparatus for forming a uniform film of thermoplastic material on a conductive support member supported by a planar support mounted on a divisable turntable located in a housing which includes a dispenser mounted therein for delivering a charge of fluent material onto the member to be coated such that rotation of the member by the planar support distributes the fluent material radially outward coating the member.
In each of the apparatus described above, the centrifugal force developed by the rotation of the substrate causes the coating material to be urged toward the edge of the rotating surface to be coated. Where the material being coated is a substrate, an edge surface discontinuity exists in the surface tension of the film of coating material. As the centrifugal force urges the coating material toward the edge, the surface tension of the film causes a bulge in the edge of the film resulting in an edge accumulation of the coating material on the surface. After the coating material, such as the photoresist material, is dried, the substrate is usually trimmed to remove the edge accumulation.
In the specific application of coating a film of photoresist material on a substrate or wafer, it is desired to eliminate the edge accumulation at the edge of the substrate or wafer. One method used to eliminate the edge build-up is to machine a chamber around the edge of the substrate.
U.S. Pat. No. 4,086,870 discloses a novel photoresist material spinning head which uses a tapered top plate having a knife-edge contact to the surface of a substrate or wafer so as to seal the top of the wafer and prevent the photoresist material from flowing under the top. The knife-edge guides the excess photoresist material during spinning, onto the tapered top surface on the edge, which results in the excess photoresist material being spun off of the head.
The use of a vacuum to clamp workpieces while the same are being transported from a holding position into a working position is well known in the art. For example a positioning device for a flat rectangular workpiece using a vacuum for clamping such workpiece, such as a photograhic slide, during transporting thereof is disclosed in U.S. Pat. No. 3,950,095.
A blade and vacuum used for removing excess coating material scraped by the blade from a smoothing rod after the smoothing rod has coated a surface of a drum with developing powder are shown in U.S. Pat. No. 3,609,029.